Seeded emulsion polymerization of α-methylstyrene and acrylonitrile

Abstract

An α-methylstyrene/acrylonitrile copolymer obtainable by emulsion polymerization which, in combination with other polymers, particularly PVC, enables alloys of outstanding thermal stability and color stability to be produced and, in addition, has a high heat distortion temperature and shows good fogging behavior and which is obtained by radically initiated inflow copolymerization of a mixture of 30 to 32 parts by weight acrylonitrile and 68 to 70 parts by weight α-methylstyrene in the presence of an emulsifier containing carboxyl groups. The polymerization is conducted in such a way that a seed latex of the same copolymer or of an analogous copolymer is introduced before addition of the monomers is commenced, the reaction temperature is kept between 75° and 82° C. and the molar ratio of emulsifier to initiator is between 4 and 6.

We claim: 
     
       1. A process for the production of copolymer which comprises the polymerisation of from 30 to 32 parts by weight, of acrylonitrile and from 68 to 70 parts, by weight, of α-methyl-styrene, the monomers being introduced into a seed latex comprising an (α-methyl)-styrene/acrylonitrile copolymer and the polymerization being effected in the presence of a radical water-soluble initiator and a carboxyl group-containing emulsifier at a temperature of from 75° to 82° C., such that the molar ratio of emulsifier:initiator is from 4:1 to 6:1. 
     
     
       2. A process as claimed in claim 1 wherein from 0.1 to 3.5%, by weight, solid/solid based on the copolymer product, of seed latex is used. 
     
     
       3. A process as claimed in claim 1, wherein from 0.2 to 1.0%, by weight, based on 100 parts, by weight, of the copolymer product, of initiator is used. 
     
     
       4. A process as claimed in claim 1, wherein from 2.0 to 2.8%, by weight, based on 100 parts, by weight, of the copolymer product, of emulsifier is used.